The purpose of this study is to examine the uses of fly ash asa type of construction material. This paper presents the results of research performed to identify optimum mix proportions for production of lowable fill with high volume fly ash content . The fly ash used in this study met the requirements of KS L 5405 and ASTM C 618 for Class F material. The flowable fill with high volume fly ash content was investigated for strength and flowability characteristics. Tests were carried out on flowable fill designed to have 10 ~15kgf/$ extrm{cm}^2$ compressive strength at 28 days with fly ash contents of approximately 260kgf/㎥. Slump was held at 25$pm$1cm for all mixtures produced to range from 5kgf/$ extrm{cm}^2$ to 14kgf/$ extrm{cm}^2$ compressive strengths at 28 days. To produce flowable fill with high volume fly ash , first the influential variables were identified in an experimental study based on factorial design. Among the proportioning variables investigated, cement ,fly ash, and sand contents were found to have statistically significant effect on strength and slump of flowable fill . Subsequently, response surface analysis techniques were used to devise an experimental program that helped determine the optimum combinations of the selected influential variables based on material properties and cost. The optimized flowable fill were then technically evaluated. It is shown that flowable fill has acceptable compressive strength , slump flow, hardening time, and permeability.